Abstract
DNA vaccines have been widely employed in controlling viral and bacterial infections in mammals and teleost fish. Co-injection of molecular adjuvants, including chemokines, cytokines, and immune co-stimulatory molecules, is one of the potential strategies used to improve DNA vaccine efficacy. In mammals and teleost fish, interleukin-34 (IL-34) had been described as a multifunctional cytokine and its immunological role had been confirmed; however, the adjuvant capacity of IL-34 remains to be elucidated. In this study, IL-34 was identified in largemouth bass. A recombinant plasmid of IL-34 (pcIL-34) was constructed and co-administered with a DNA vaccine encoding hypoxic response protein 1 (Hrp1; pcHrp1) to evaluate the adjuvant capacity of pcIL-34 against Nocardia seriolae infection. Our results indicated that pcIL-34 co-injected with pcHrp1 not only triggered innate immunity and a specific antibody response, but also enhanced the mRNA expression level of immune-related genes encoding for cytokines, chemokines, and humoral and cell-mediated immunity. Moreover, pcIL-34 enhanced the protection of pcHrp1 against N. seriolae challenge and conferred the relative percent survival of 82.14%. Collectively, IL-34 is a promising adjuvant in a DNA vaccine against nocardiosis in fish.
Highlights
Nocardiosis, caused by the facultative intracellular bacteria Nocardia seriolae, is a problematic infection in the fish aquaculture industry and leads to severe economic loss in Asian countries, especially Taiwan, China, Japan, and Vietnam [1–5]
The first 25 a.a. were predicted as signal peptides and three potential N-glycosylation sites were found in the largemouth bass (LMB)-IL-34 sequence
The C-terminal tail of LMB-IL-34 is about 29 a.a. shorter than human IL-34, which contains an enriched region of proline-serine-threonine (Pro-Ser-Thr), a typical characteristic of flexible mucin-like O-linked glycosylation-rich sequences that are absent in teleost species [55]
Summary
Nocardiosis, caused by the facultative intracellular bacteria Nocardia seriolae, is a problematic infection in the fish aquaculture industry and leads to severe economic loss in Asian countries, especially Taiwan, China, Japan, and Vietnam [1–5]. Nocardiosis treatment relies mainly on chemical and pharmaceutical therapies; the use of these compounds can lead to contamination of the aquatic environment, accumulation of antibiotics in the fish body, and appearance of drug-resistance bacteria. A DNA vaccine encompasses a gene delivered from pathogenic viruses or bacteria, encoding an immunogenic protein and a vector with a eukaryotic cell promoter, to help drive protein expression. Compared with traditional inactivated and subunit vaccines, DNA vaccines have been documented to stimulate a robust cytotoxic T cell response. DNA vaccines can induce both humoral and cellular adaptive immune responses by evolving with major histocompatibility complex (MHC)
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